Field of the Invention
The invention pertains to a temperature sensor for measuring temperatures within a defined temperature measuring range. The sensor has the following features:
a reference voltage source for providing a reference voltage at an output terminal which is connected to a first input terminal of a comparator; PA1 a series circuit of a measuring element and a reference component connected between a first and a second supply terminal, whereby a temperature-dependent voltage is applied to a node common to the semiconductor component and the reference component and is applied to a second input terminal of the comparator.
Such kinds of temperature sensors, in particular those fabricated in an integrated way, are used for switching, especially for switching off loads if a specified temperature is exceeded. For this purpose the temperature-dependent voltage and the reference voltage are compared through a comparing element usually realized as a comparator, whereby one of two different voltage levels is applied to the output of the comparator depending on whether or not the temperature-dependent voltage is higher than the reference voltage.
A temperature sensor of this kind is known from the commonly assigned invention described in German published patent application DE 44 37 461 A1. The reference voltage source is thereby formed as a series circuit between a first supply terminal and a second supply terminal. The series circuit has a depletion-mode FET wired up as a current source and an enhancement-mode FET wired up as a diode. A node common to the depletion-mode FET and the enhancement-mode FET is thereby connected as the reference voltage output to a first input terminal of the comparator. The two transistors in that prior art temperature sensor are dimensioned such that the reference voltage remains constant within the temperature range to be measured, or increases with increasing temperature. The reference component in the known temperature sensor is realized as a depletion-mode FET which is wired up as a current source. The measuring element connected in series with the reference component has a temperature-dependent current characteristic and is formed as a series circuit of two enhancement-mode FETS, each of which is wired up as a diode. A node common to the depletion-mode FET and the series circuit of the enhancement-mode FET is connected to a second input of the comparator, whereby the depletion-mode FET serving as reference component and the enhancement-mode FET connected in series thereto are tuned to each other such that the potential applied to this node decreases with increasing temperature in order to cause a change of the voltage level at the output of the comparator in the event that this potential falls below the reference voltage delivered by the reference voltage source.
In the prior art temperature sensor, the switching temperature, i.e. the temperature at which the temperature-dependent voltage attains the value of the reference voltage, is defined exclusively through the dimensioning of the components.